Synthetic polymers prepared by polymerization of monomers in aqueous emulsion may be recovered as the solid product, dried and used as such. It has long been known that synthetic polymers prepared by free radical emulsion polymerization may be recovered as the solid product by coagulation by contact with an inorganic salt or an inorganic salt plus an acid, followed by separation of the coagulated polymer from the aqueous phase and subsequent drying of the separated polymer. Commonly used coagulation materials include as examples of the inorganic salts, sodium chloride, calcium chloride, magnesium sulphate, alum, etc., and as examples of inorganic salt plus acid, sodium chloride plus sulphuric, hydrochloric or acetic acid. Using such materials leads to problems with disposal of the separated aqueous phase due to the presence therein of the various inorganic components. An alternative system of coagulation uses an acid, especially inorganic acids such as sulphuric or hydrochloric acid, and animal-derived glue as an additive--however, the coagulation efficiency is very variable with this system as evidenced by the presence of a relatively large amount of small particles in the separated aqueous phase, and the coagulated polymer frequently takes the form of very small-sized particles which are difficult to separate completely from the aqueous phase and which are difficult to dry to low residual moisture levels. A further alternative system of coagulation has been to use an inorganic acid, especially sulphuric or hydrochloric acid, and lignin as an additive--due to the dark color associated with lignin, this system is not suitable for use where normal light-colored polymers are required. Another system of coagulation is the addition of fairly large amounts of starch xanthate or pregelatinized cereal grain polysaccharide material to the polymer emulsion and co-precipitation of the polymer and additive by the addition of zinc chloride or sulphate or other mineral acid salts of divalent metals--the product from this system contains a fairly high proportion of non-polymer constituents which is not desirable nor commercially acceptable for all polymers. Reinforced polymers have been prepared by coagulation by contact with inorganic acid and alkali earth metal salts, of polymer emulsions in the presence of starch xanthate or cereal flour xanthate, which xanthates have previously been treated with resorcinol and formaldehyde--these polymers contain at least 30 parts by weight of the treated starch or cereal flour xanthate per 100 parts by weight of the polymer.